How Ignoring Your Biological Clock Contributes to Weight Gain

shutterstock_48207385Most people schedule their activities based on an external clock. They go to work at a certain time and eat and sleep at certain hours of the day. But all animals, including humans, have another type of clock – an internal biological clock. This clock operates on a 24-hour cycle to determine eating and sleeping cycles. Unlike animals, humans have the power to override their internal biological clock or circadian rhythms by ignoring those internal signals. Many do by staying up after dark and doing a little late-night snacking when they should be sleeping.

People who do shift work and night shifts “confuse” their biological clock even more by sleeping during the day and remaining awake at night. Unfortunately, there’s more and more evidence suggesting that this type of “internal conflict” contributes to weight gain, obesity, and other health issues. Are your late night habits making it harder for you to lose weight?

Ignoring Your Biological Clock Could Slow Down Your Metabolism

At the Brigham and Women’s Hospital in Boston, researchers put 21 participants through a series of sleep cycles mimicking the sleep schedules of rotating shift workers and travelers crossing time zones. These cycles forced participants to sleep and stay awake at times that would conflict with their natural 24-hour circadian rhythms. The result? During the periods the participants slept irregularly, their metabolic rate dropped by 8% even though they ate a similar diet and got a similar amount of activity. Just as concerning, their blood glucose levels rose to near diabetic levels during the periods their natural sleep patterns were disrupted.

Light at Night Could It More Difficult to Control Weight

You don’t need to be a shift worker to experience the negative effects of altered circadian rhythms. People who stay up late at night studying or watching television are also at conflict with their natural biological clocks. Artificial lights late at night disrupt circadian rhythms by altering hormones that affect sleep, fertility and overall health, like melatonin. They also disrupt hormones that control food how much you eat as well.

When mice were exposed to light at night while sleeping over a two-month period, they gained 50% more weight than mice that slept in total darkness. In humans, irregular sleep raises levels of the hormone ghrelin that increases hunger and lowers levels of leptin, another appetite-regulating hormone. This increases cravings for starchy foods and boosts appetite in general. The same thing happens when you “burn the midnight oil” and expose your eyes to light when your body expects to be asleep. Plus, light exposure at night blocks the production of melatonin by the pineal gland in your brain. This has been linked with a greater risk of some types of cancer, particularly breast cancer in women.

What Does This Mean?

If you’re staying up late at night, getting inadequate sleep or sleeping with light in your room, you’re disrupting your body’s natural circadian rhythms. This could make it more challenging to control your weight by slowing down your metabolism and increasing cravings for unhealthy foods. Here are some tips for avoiding this problem:

Try to get to bed no later than 10:00 P.M. at night. If you can’t make the transition all at once, gradually transition to an earlier bedtime.

Go to sleep and wake up at the same time every day even on weekends.

Remove all light sources from your room. Even small amounts of light from an electrical clock or light coming underneath a door can disrupt melatonin levels and alter your internal biological clock.

Wear a light-blocking mask over your eyes when you sleep if you can’t remove all light from your room.

Don’t turn the light on when you go to the bathroom at night. Even brief periods of light exposure disrupt melatonin levels.

The Bottom Line?

There are disadvantages to being a night owl. It could make it more difficult to control your weight. Stay in sync with your natural biological clock by going to bed as early as possible and sleeping in total darkness. It’s another small change you can make to control your appetite and you’re your waistline.



Journal of the American Medical Association – News at JAMA. “Disrupting Body’s Biological Clock May Increase Risk of Weight Gain, Diabetes’
Mercola.com. “Make This Common Mistake While Sleeping and Risk Gaining Weight”
Breast Cancer Fund. “Light at Night and Melatonin”


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